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Freiburg, Germany

The Kiepenheuer Institute for Solar Physics is a research institute located in Freiburg, Germany. Its research focuses on the exploration of the Sun and heliosphere. The institute has one solar telescope on the Schauinsland Mountain near Freiburg and, in collaboration with other institutions, uses solar telescopes of the Teide Observatory in Tenerife, Spain. Wikipedia.

Franz M.,Kiepenheuer Institute for Solar Physics
Astronomische Nachrichten | Year: 2012

A precise knowledge of the surface structure of sunspots is essential to construct adequate input models for helioseismic inversion tools. We summarize our recent findings about the velocity and magnetic field in and around sunspots using HINODE observation. To this end we quantize the horizontal and vertical component of the penumbral velocity field at different levels of precision and study the moat flow around sunspot. Furthermore, we find that a significant amount of the penumbral magnetic fields return below the surface within the penumbra. Finally, we explain why the related opposite polarity signals remain hidden in magnetograms constructed from measurements with limited spectral resolution. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Borrero J.M.,Kiepenheuer Institute for Solar Physics | Ichimoto K.,Kyoto University
Living Reviews in Solar Physics | Year: 2011

In this review we give an overview about the current state-of-knowledge of the magnetic field in sunspots from an observational point of view. We start by offering a brief description of tools that are most commonly employed to infer the magnetic field in the solar atmosphere with emphasis in the photosphere of sunspots. We then address separately the global and local magnetic structure of sunspots, focusing on the implications of the current observations for the different sunspots models, energy transport mechanisms, extrapolations of the magnetic field towards the corona, and other issues. Source

Borrero J.M.,Kiepenheuer Institute for Solar Physics | Kobel P.,Max Planck Institute for Solar System Research
Astronomy and Astrophysics | Year: 2011

In the past, spectropolarimetric data from Hinode/SP were employed to infer the distribution of the magnetic field vector in the quiet Sun. While some authors found predominantly horizontal magnetic fields, others favor an isotropic distribution. We investigate whether it is actually possible to accurately retrieve the magnetic field vector in regions with very low polarization signals (e.g. internetwork), employing the FeI line pair at 6300 A. We first perform inversions of the Stokes vector observed with Hinode/SP in the quiet Sun at disk center in order to confirm the distributions retrieved by other authors. We then carry out several Monte-Carlo simulations with synthetic data, with which we show that the observed distribution of the magnetic field vector can be explained in terms of purely vertical (γ = 0°) and weak fields ( β > 20 G), which are misinterpreted by the analysis technique (Stokes inversion code) as being horizontal (γ ≈ 90°) and stronger ( β ≈ 100 G), owing to the effect of the photon noise. This challenges the correctness of previous results, which presented the distributions for the magnetic field vector peaking at γ = 90° and β = 100 G. We propose that an accurate determination of the magnetic field vector can be achieved by decreasing the photon noise to a point where most of the observed profiles posses Stokes Q or U profiles that are above the noise level. Unfortunately, for noise levels as low as 2.8 × 10-4, only 30 % of the observed region with Hinode/SP have sufficiently strong Q or U signals, implying that the magnetic field vector remains unknown in the rest of the internetwork. © 2011 ESO. Source

Agency: Cordis | Branch: FP7 | Program: CP-FP | Phase: SPA.2012.2.1-01 | Award Amount: 3.22M | Year: 2013

Observations of oscillations on the solar and stellar surfaces have emerged as a unique and extremely powerful tool to gain information on, and understanding of, the processes in the Sun and stars, and the origin of the variability in the solar and stellar output. Through helio- and asteroseismology detailed inferences of the internal structure and rotation of the Sun, and extensive information on the properties of a broad range of stars can be obtained. Space-based observations play a leading role in helio- and asteroseismology, in close synergy with ground-based observations as well as theoretical modelling. Long observing sequences are essential for measuring the oscillation frequencies with the precision required, and to extract the lowest mode frequencies involved. The enormous value of long-term space-based observations has been demonstrated in the solar case by the joint ESA/NASA SOHO mission (Solar and Heliospheric Observatory. This is now being followed by instruments on the NASA Solar Dynamics Observatory (SDO) mission.Large volumes of exquisite data on stellar oscillations of stars with a broad range of masses and ages are being collected by the CNES space mission CoRoT (Convection, Rotation and Transit) and the NASA Kepler mission. Extensive Earth-based observations of solar oscillations have been undertaken with the GONG network (Global Oscillations Network Group) and the Birmingham Oscillation Network (BiSON) to ensure continuous monitoring. A asteroseismic network, SONG (Stellar Observations Network Group) is being established under Danish leadership. Equally important for asteroseismology is the availability of supplementary data on the stars from more traditional observations, to determine their surface temperature, composition, radius, etc. Only through a coordinated use of the space- and ground-based data can the full potential of helio- and asteroseismology be realized.

Siegel D.M.,Max Planck Institute for Physics | Roth M.,Kiepenheuer Institute for Solar Physics
Astrophysical Journal | Year: 2014

The universe is expected to be permeated by a stochastic background of gravitational radiation of astrophysical and cosmological origin. This background is capable of exciting oscillations in solar-like stars. Here we show that solar-like oscillators can be employed as giant hydrodynamical detectors for such a background in the μHz to mHz frequency range, which has remained essentially unexplored until today. We demonstrate this approach by using high-precision radial velocity data for the Sun to constrain the normalized energy density of the stochastic gravitational-wave background around 0.11 mHz. These results open up the possibility for asteroseismic missions like CoRoT and Kepler to probe fundamental physics. © 2014. The American Astronomical Society. All rights reserved. Source

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